[MLIR] Add booleans to dense element list in LangRef

[bollu]

Summary

Add boolean values as a dense element, as tested in the MLIR parser:

// CHECK: "splatBoolTensor"() {bar = dense<false> : tensor<i1>} : () -> ()
"splatBoolTensor"(){bar = dense<false> : tensor<i1>} : () -> ()

https://github.com/llvm/llvm-project/blob/43d758b142bbdf94a1c55dc0950637ae74f825b9/mlir/test/IR/parser.mlir#L630-L631

mlir/include/mlir/IR/BuiltinAttributes.td

def Builtin_DenseIntOrFPElementsAttr : Builtin_Attr<
     "DenseIntOrFPElements", [ElementsAttrInterface], "DenseElementsAttr"
   > {
   let summary = "An Attribute containing a dense multi-dimensional array of "
                 "integer or floating-point values";
   let description = [{
     Syntax:
 
     ```
-    tensor-literal ::= integer-literal | float-literal | [] | [tensor-literal (, tensor-literal)* ]
+    tensor-literal ::= integer-literal | float-literal | bool-literal | [] | [tensor-literal (, tensor-literal)* ]
     dense-intorfloat-elements-attribute ::= `dense` `<` tensor-literal `>` `:`
                                             ( tensor-type | vector-type )
     ```
 
     A dense int-or-float elements attribute is an elements attribute containing
     a densely packed vector or tensor of integer or floating-point values. The
     element type of this attribute is required to be either an `IntegerType` or
     a `FloatType`.